1. Field of the Invention
The present invention relates to an anti-reflective coating. In particular, the present invention relates to an anti-reflective coating that can be used to increase the light transmission of glass used in the manufacture of solar modules, and to a method of making the anti-reflective coating.
2. Discussion of the Background
All United States Patents and Application Publications referred to herein are incorporated by reference in their entireties. In the case of conflict, the present specification, including definitions, will control.
Solar modules have been developed that convert light into electricity. These modules typically include an outer layer of glass. The difference in the index of refraction between the glass and air can lead to an undesirable partial reflection of light from the glass that reduces the amount of incident light that can be converted into electricity by the module.
Some success at reducing the reflection has been achieved by forming low index of refraction coatings of silica on the glass. U.S. Pat. No. 7,128,944 discloses low index silica coatings formed by coating the glass with an aqueous coating solution and a surfactant mixture, the aqueous coating solution having a pH of 3 to 8, containing 0.5 wt. % to 5.0 wt. % [SiOx(OH)y]n having a particle size of 10 nm to 60 nm, and a surfactant mixture; drying the coated glass; thermal toughening at temperatures of at least 600° C.; and thermal tempering of the coated glass by a forced air flow.
Other low index silica coatings have been formed by dipping a glass substrate in a mixture of tetraethyl orthosilicate and ethanol to form a liquid film on the glass, or by spraying on the glass a mixture of tetraethyl orthosilicate and ethanol to form a liquid film; evaporating the ethanol from the liquid film to form a film residue; and then heating the film residue to convert the tetraethyl orthosilicate into silica. Including polyethylene glycol in the liquid films has been found to create pores in the silica films during the heating that further lower the index of refraction of the silica and increases light transmission.
However, silica coatings formed using liquid films containing tetraethyl orthosilicate, polyethylene glycol and ethanol have not shown a consistent improvement in transmission. Accordingly, there is a need in the art for anti-reflection films that achieve improved properties with consistency and methods of preparing such films.